Entropy and Gravity

Grøn, Øyvind

doi:10.3390/e14122456

Cited by 16 publications

(27 citation statements)

References 36 publications

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“…phenomenon. A review of entropy and gravity, which also comprises a section on the entropy of black holes, is found in [16].…”

Section: Sharp Interface Description Of a Geometric Objectmentioning

confidence: 99%

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Entropy and Geometric Objects

Schmitz

2018

Entropy

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Different notions of entropy can be identified in different scientific communities: (i) the thermodynamic sense; (ii) the information sense; (iii) the statistical sense; (iv) the disorder sense; and (v) the homogeneity sense. Especially the "disorder sense" and the "homogeneity sense" relate to and require the notion of space and time. One of the few prominent examples relating entropy to both geometry and space is the Bekenstein-Hawking entropy of a Black Hole. Although this was developed for describing a physical object-a black hole-having a mass, a momentum, a temperature, an electrical charge, etc., absolutely no information about this object's attributes can ultimately be found in the final formulation. In contrast, the Bekenstein-Hawking entropy in its dimensionless form is a positive quantity only comprising geometric attributes such as an area A-the area of the event horizon of the black hole, a length L P-the Planck length, and a factor 1/4. A purely geometric approach to this formulation will be presented here. The approach is based on a continuous 3D extension of the Heaviside function which draws on the phase-field concept of diffuse interfaces. Entropy enters into the local and statistical description of contrast or gradient distributions in the transition region of the extended Heaviside function definition. The structure of the Bekenstein-Hawking formulation is ultimately derived for a geometric sphere based solely on geometric-statistical considerations.

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“…phenomenon. A review of entropy and gravity, which also comprises a section on the entropy of black holes, is found in [16].…”

Section: Sharp Interface Description Of a Geometric Objectmentioning

confidence: 99%

“…The formulation of the entropy of a black hole plays an important role in the holographic principle [12,13] and in current entropic-gravity concepts [14,15] describing gravity as an emergent phenomenon. A review of entropy and gravity, which also comprises a section on the entropy of black holes, is found in [16].…”

Section: Introductionmentioning

confidence: 99%

Entropy and Geometric Objects

Schmitz

2018

Entropy

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“…There are several conjectures as to what the maximal entropy of the Universe may be [16]. One is the so-called Bekenstein bound [17].…”

Section: The Concept Of a Maximal Entropy For The Universementioning

confidence: 99%

Gravitational Entropy and Inflation

Elgarøy

Grøn

2013

Entropy

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Abstract:The main topic of this paper is a description of the generation of entropy at the end of the inflationary era. As a generalization of the present standard model of the Universe dominated by pressureless dust and a Lorentz invariant vacuum energy (LIVE), we first present a flat Friedmann universe model, where the dust is replaced with an ideal gas. It is shown that the pressure of the gas is inversely proportional to the fifth power of the scale factor and that the entropy in a comoving volume does not change during the expansion. We then review different measures of gravitational entropy related to the Weyl curvature conjecture and calculate the time evolution of two proposed measures of gravitational entropy in a LIVE-dominated Bianchi type I universe, and a Lemaitre-Bondi-Tolman universe with LIVE. Finally, we elaborate upon a model of energy transition from vacuum energy to radiation energy, that of Bonanno and Reuter, and calculate the time evolution of the entropies of vacuum energy and radiation energy. We also calculate the evolution of the maximal entropy according to some recipes and demonstrate how a gap between the maximal entropy and the actual entropy opens up at the end of the inflationary era.

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“…Then, using the Clausius-Caratheodory concept of the temperature as the integrating factor for the heat we can calculate the entropy of each component of the cosmological fluid. The entropy of the universe has been discussed in many papers [2,6,7,8,9,10,11,12]. The discussion concerned mainly non-interacting fluids.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics of diffusive DM/DE systems

Haba¹

2017

Gen Relativ Gravit

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We discuss the energy density,temperature and entropy of dark matter (DM) and dark energy (DE) as functions of the scale factor $a$ in an expanding universe. In a model of non-interacting dark components we repeat a derivation from thermodynamics of the well-known relations between the energy density,entropy and temperature. In particular, the entropy is constant as a consequence of the energy conservation. We consider a model of the DM/DE interaction where DM energy density increase is proportional to the particle density. In such a model the dependence of the energy density and the temperature on the scale factor $a$ is substantially modified. We discuss (as a realization of the model) DM which consists of relativistic particles diffusing in an environment of DE. The energy gained by the dark matter comes from a cosmological fluid with a negative pressure. We define the entropy and free energy of such a non-equilibrium system. We show that during the universe evolution the entropy of DM is increasing whereas the entropy of DE is decreasing. The total entropy can increase (in spite of the energy conservation) as DM and DE temperatures are different. We discuss non-equilibrium thermodynamics on the basis of the notion of relative entropy.Comment: 20 page

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Entropy and Gravity

Cited by 16 publications

References 36 publications

Entropy and Geometric Objects

Entropy and Geometric Objects

Gravitational Entropy and Inflation

Thermodynamics of diffusive DM/DE systems

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